Fig. 3.

Diagrammatic representation of a longitudinal section through the vein (may be relevant to human saphenous vein) showing the venal bicuspid valves with their cusps/leaflets closed. Note that the agger is located at the base of valves. Large arrow indicates the main direction (against gravity) of blood movement, while the two small arrows, above valves, indicate a backflow of blood, in particular if valves are damaged in pathological conditions, and where the thickening of agger's structure (usually comprising smooth muscle and elastin) also occurs. For more details about venal valve and agger, see, e.g,. Corcos et al.^[31], 2000, and Crotty^[8], 2011.